Sunrise 6:56 AM   Sunset 8:15 PM Moonrise 3:28 PM   Moonset 4:05 AM

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FXUS64 KMRX 191145 AFDMRX

Area Forecast Discussion National Weather Service Morristown TN 745 AM EDT Fri Apr 19 2024

New AVIATION

SHORT TERM
(Today and tonight)
Issued at 307 AM EDT Fri Apr 19 2024

Key Messages:

1. Scattered showers and a few thunderstorms move in through this morning. A few strong storms are possible.

2. A second round of scattered strong thunderstorms this afternoon across the Tennessee valley. Gusty winds and large hail possible with the afternoon thunderstorms.

Discussion:

A few showers and storms will move through the area this morning.
CAMS show isolated to scattered activity moving onto the Cumberland Plateau between 07 and 08Z, then spreading eastward into the east TN Valley through sunrise. This is in response to 500mb vorticity moving through the area ahead of a cold front located back across west TN. Current meso-analysis shows a few hundred joules of CAPE west of I-75, which is where a few storms are expected through sunrise. Given the weak insatiability field, don't expect any severe weather during this timeframe but an isolated strong storm can't be ruled out.

After sunrise, isolated showers and a few storms will remain possible through late morning across the whole forecast area.
Instability begins to increase from late morning and into the afternoon hours with daytime heating. HRRR mean ensemble SBCAPE values for this afternoon range between 1000 and 1500 J/kg. This coincides with when the cold front will be moving through the area.
This results in showers and storms increasing in coverage as the front passes through. Isolated damaging wind gusts up to 60 mph and hail from 1 to 1.25" will be the primary threats this afternoon with any stronger storms. The larger hail sizes are due to steep mid level lapse rates along with moderate 0-6km shear of 30 to 40kts.
The 0-6km shear will increase the residence time of hail in the updrafts of any stronger storms. The shear in the lowest levels is very weak today, thus removing the threat of tornadoes. SPC currently has most of our area under a marginal risk for severe storms.

LONG TERM
(Saturday through Thursday)
Issued at 307 AM EDT Fri Apr 19 2024

Key Messages:

1. Outside of rain chances Sunday, drier and cooler conditions are expected into early next week, especially Monday.

2. Rain chances and more seasonal temperatures will return by Wednesday and Thursday.

Discussion:

By Saturday a surface front will have exited the area to the southeast as the upper level pattern becomes quasi-zonal. Northerly surface winds will bring drier and cooler air to the region. A weak shortwave disturbance translating through the mean flow will bring a return to precipitation chances Sunday, however, this will generally remain restricted to areas along and south of Interstate-40. Mean ensemble guidance probability of 24 hour precipitation GTE to a tenth of an inch is 50-70%. Probability for GTE half an inch is 20% or less. Some patchy frost will be possible Sunday night, with temperatures falling into the mid to upper 30s. The question will be if winds lighten enough with the shortwave traversing the area.

Dry conditions with a warming trend will kick off the new work week.
The next chance for some additional light rain showers will come Wednesday as a trough digs into the Ohio Valley. Better forcing remains well to our north, leading to only light precipitation. For Wednesday, mean ensemble guidance probability of 24 hour precipitation GTE to a tenth of an inch is only 30-60%. High pressure builds in behind the front Wednesday, with returning dry conditions.

AVIATION
(12Z TAFS)
Issued at 742 AM EDT Fri Apr 19 2024

Mostly VFR conditions this morning at all sites, except for a few hours of TEMPO MVFR through late morning. Additional scattered showers and storms develop this afternoon and PROB30 MVFR conditions are in at all sites. MVFR conditions are likely later tonight and will last through the end of the period.

PRELIMINARY POINT TEMPS/POPS
Chattanooga Airport, TN 80 57 72 50 / 50 10 10 20 Knoxville McGhee Tyson Airport, TN 75 54 68 48 / 80 20 10 10 Oak Ridge, TN 77 53 69 47 / 70 10 10 10 Tri Cities Airport, TN 73 51 66 44 / 100 20 10 10

MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...NONE.
VA...NONE.

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